In accordance with Long Term Evolution (LTE) specified in the 3rd Generation Partnership Project (3GPP), an inter base-station handover (X2-HO) is specified (for example, Non-Patent Document 1) such that when a mobile station (UE) performs a handover from a radio base station (eNB) #1 to an eNB#2, data addressed to the UE and transmitted to the eNB#1 from a core network (specifically, a Serving Gateway (S-GW)) shall be relayed from the eNB#1 to the eNB#2 by using an inter base-station transmission path (X2) provided between the eNBs.
FIG. 1 illustrates a communication sequence of such a conventional inter base-station handover. In addition, FIGS. 2(a) and 2(b) illustrate data transfer routes to a UE before and after an inter base-station handover.
As illustrated in FIG. 1, the eNB#1 transmits X2-AP: HANDOVER REQUEST to the eNB#2 based on a measurement result (RRC: MEASUREMENT REPORT) of a radio environment received from the UE (S10), and then a handover to the eNB#2 is executed (S20 to S60). After completion of such an inter base-station handover, data addressed to the UE is transmitted to the UE via an S-GW, the eNB#1 and the eNB#2.
Thereafter, the eNB#2 sends a Mobility Management Entity (MME) S1-AP: PATH SWITCH REQUEST which requests to switch from a trunk transmission path (S1) between the eNB#1 and the S-GW (S70). The MME having received S1-AP: PATH SWITCH REQUEST sends S1-AP: PATH SWITCH REQUEST ACKNOWLEDGE to the eNB#2 (S80), and performs control such that a highway (HWY) to which data addressed to the UE is to be transferred, that is, the transmission path between the eNB and the S-GW can be switched from the path to the eNB#1 to the path to the eNB#2. As a result, as illustrated in FIG. 2(b), data is transferred to the UE via the HWY connected to the eNB#2.